Applicant's U.S. Pat. No. 4,314,408 concerned a drafting instrument which combined a graphics tube having a limited number of engineering, architectural and other linear scales being rotatably mounted in an outer tubular body with a straightedge magnifier and a compass assembly. The present invention provides an improved housing having two rotatable shafts. A transparent Mylar sheet having a large number of scales thereon is attached to the rotatable shafts. Multiple scales are contained on the transparent Mylar sheet. Each scale may be brought into alignment with a viewing window so that it can be individually viewed.
Each graphics tube of the embodiment shown in U.S. Pat. No. 4,314,408 is limited to a maximum of about 20 scales. If, for example, 150 different scales are needed or desired, then 8 different graphics tubes would have to be purchased by the draftsman. In the present illustrated improved embodiment, 150 different scales may all be placed on a single graphics sheet and combined into a single self-contained instrument.
In the past, normal drafting procedures have required several tools having a variety of scales. It has been common for a draftsman to be required to purchase separately an architectural scale, an engineering scale and other scales in order to perform most ordinary drafting procedures. Not only is the purchase of all of the above instruments relatively expensive, but the utilization of so many instruments has necessitated frequent searching around the working area for the proper instrument. The invention disclosed herein combines multiple scales into a single self-contained package. An accurate cursor is provided for convenient accurate viewing of the scales.
In the past, drafting work has been very tedious and tiring to the eyes and has required a number of physical motions and procedures because numerous scales and numerous tools were required in order to perform most such drafting procedures. Frequent searching for the proper scales or other instruments around the working area has been required as a draftsman reaches a step in the procedure which requires a different scale. Thus, a need has existed for a single, inexpensive drafting tool which is accurate and which provides the necessary scales to perform most drafting procedures without the need for additional scales. The prior art arrangements have failed to disclose a single tool which could replace the need for separately purchasing an architect scale, an engineering scale, a plurality of map scales, an "80" scale, a millimeter scale, and a large number of other scales.
Applicant's U.S. Pat. No. 4,314,408 provided for increasing the number of scales by changing a replaceable graphics tube. The present invention is an improvement over that patent by providing for a large number of self-contained scales on a single transparent Mylar film. There is no need to search for additional graphics tubes when a large number of scales are needed. By turning two rotatable shafts, the Mylar film may be wound and unwound upon the shafts, respectively, to individually bring one of a large number of scales into alignment with a viewing window.
The problems enumerated above are not intended to be exhaustive. Other problems may also be apparent from the following detailed description of a preferred embodiment.